An automotive vehicle typically includes an engine having a crankshaft that transfers power from the engine and through a driveshaft to turn the wheels. A transmission may be interposed between the engine and the driveshaft to regulate torque and speed ratios between the crankshaft and the driveshaft. In a manually-operated transmission, a manually operated clutch may be interposed between the engine and the transmission to allow controlled disengagement of the crankshaft and the driveshaft and enable shifting between available transmission gear ratios. In an automatic transmission, a series of clutch assemblies, or clutch modules, may be positioned behind a torque converter assembly along the power path leading from the engine to the wheels, and they may be adapted to dynamically shift between available gear ratios without requiring driver intervention.
In general, a clutch assembly may include a hub, an alternating sequence of friction plates and reaction plates (or separator plates), and an outer housing surrounding the hub and the alternating sequence of friction plates and reaction plates. A wet clutch assembly (as opposed to a dry clutch assembly) may further include a transmission fluid which flows through the clutch assembly. In some arrangements, each of the friction plates may be splined to and rotatable with the hub, while each of the reaction plates may be splined to the outer housing, although the opposite arrangement is also possible. When the clutch assembly is in an open position, the reaction plates and the friction plates may be spaced apart and capable of rotating at different speeds and/or in different directions independently of each other. When the clutch assembly is activated, the clutch assembly is shifted to a closed position in which the friction plates and the reaction plates are pressed together to restrict their relative rotations.
A torque converter clutch assembly in an automatic transmission is a device capable of transferring torque from the engine to the transmission. A torque converter assembly may include a front cover plate connected to the engine, an impeller connected to a front cover plate, a turbine connected to an input shaft of the transmission, a stator, at least one piston plate attached to the turbine and interposed between the turbine and the front cover plate. In addition, it may also include a transmission fluid flowing through the assembly, as well as various additional components. In operation, power from the engine may be transmitted to the impeller via the front cover, causing the impeller to revolve and push transmission fluid against the turbine. In turn, the turbine may revolve and transmit power to the input shaft of the transmission. The torque converter assembly may be capable of selectively shifting between an open position (or turbine mode in which the turbine may multiply torque) and a closed position in which the piston plate may be hydraulically pushed against the front cover plate to create a direct connection between the engine and the transmission. For example, a torque converter assembly may be in the open position (or turbine mode) to allow fast acceleration from a stop, and it may be shifted to the closed position as the vehicle gains speed.
The overall structural configuration and mechanism of clutch assemblies may be similar to those of brake assemblies, including wet brake assemblies and dry brake assemblies. In particular, a brake assembly may generally include a hub, an alternating sequence of brake plates and reaction plates (or separator plates), and an outer housing surrounding the hub and the alternating sequence of brake plates and reaction plates. A wet brake assembly may further include a brake fluid, whereas a dry brake assembly may lack a brake fluid. Each of the brake plates may be splined to and rotatable with the hub, while the reaction plates may be splined to and held stationary with the outer housing. When the brakes are applied, the brake assembly may shift from an open position in which the brake plates and the reaction plates are separated to a closed position in which the brake plates and the reaction plates are pressed together to restrict relative rotation between the plates.
While above assembly designs are effective, during the proper functioning of a clutch assembly, a torque converter clutch assembly, and a brake assembly, a substantial amount of friction-induced heat may be generated at friction interfaces between the reaction plates and friction plates/brake plates (in a clutch assembly or a brake assembly) and between the piston plate and front cover plate (in a torque converter clutch assembly) as the plates are engaged and pressed together while shifting to the closed position. The friction arises due to the relative motion between the plates as they are engaged, but will dissipate as the plates are locked-up or rotating at the same speed in the closed position. The friction-induced heat that is generated during the engagement of the plates in the aforementioned assemblies may lead to a sharp temperature rise at the friction interface(s), at least until there is no longer relative motion between the plates. As the reaction plates (in a clutch assembly and a brake assembly) and the front cover plate (in a torque converter clutch assembly) may be formed from steel or another heat-conducting metal, the generated heat will be initially absorbed on the surface of the plates. It may then be transferred to the outer housing of the assembly and/or the transmission fluid or brake fluid, and it may eventually dissipate to the surroundings. However, if temperature spikes at the friction interfaces are too high, the reaction plates or the front cover plate may undergo discoloration (or heat staining) and/or hot spotting in which localized regions of the metal material partially melt or liquefy to a molten state. In addition, friction material on the surface of the friction plates or brake plates (in a clutch assembly or a brake assembly) and on the surface of the piston plate (in a torque converter clutch assembly) may begin to deteriorate with repeated exposure to high temperatures, causing the coefficient of friction at the friction interfaces to drop. Even further, temperature-sensitive chemicals in the transmission fluid or brake fluid may also degrade upon exposure to sharp temperature spikes. Accordingly, with recurrent exposure to high temperatures caused by friction-induced heat, clutch assemblies, torque converter clutch assemblies, and brake assemblies may become damaged or even susceptible to failure.
Some prior art systems, such as U.S. Patent Application Number 2010/0013620, have incorporated temperature-sensing materials at friction linings on the surface of plates used in clutches or brakes for the purpose of detecting the operating temperature of the friction lining. However, clutch assembly, torque converter clutch assembly, and/or brake assembly designs incorporating protection mechanisms against temperature spikes at the friction interfaces between plates are still wanting.
Clearly, there is a need for strategies for managing temperatures at friction interfaces in clutch assemblies, torque converter clutch assemblies, and brake assemblies.